The idea of an elevator system with a plurality of cars in the same hoistway has been around for over 70 years. See, for example, U.S. Pat. No. Re. 18,095 by Sprague, U.S. Pat. No. 1,837,643 by J. N. Anderson, and U.S. Pat. No. 1,911,834 by D. L. Lindquist. Sprague's elevator system, which was called Dual Elevator system, was put in service in 1931 in a 20-story building in Pittsburgh. His Dual Elevator system has two independently movable cars in one shaft with the upper car serving the upper half and the lower car the lower half of the building. It is reported that the Dual Elevator system was not successful and eventually had to be taken out of service. Since then, a handful of patents have been issued on this subject, but no full blown working elevator systems of this sort have been put in service. The reason for this may be that none of the proposed systems have been able to show that they are safe enough to operate and their shaft capacity can be high enough for the price of the system.